Shelly
In any of the big Australian cities, you can easily buy a Lebara International SIM card from 7/11 type stores. There are also numerous other International SIM cards/packages available, but Lebara is, in my experience, the cheapest to the UK. (Strangely Lebara is more expensive if you call an Australian number, so keep that to a minimum)
This has an Australian mobile number, and calls to the UK cost around 2p/min to landlines, 5p/min to UK mobiles (plus, I think around 10/15p/call set up). Texts to the UK are around 10p. You pay 10 Australian Dollars for the SIM card, which is credited against calls. You have to ring them and register the card, but this is simple and just give your hotel as an Australian address. If you need to add money beyond the initial $10, you just buy a voucher, which is widly available from 7/11 type stores. From my experience coverage is fine in all of the big cities, but a bit hit & miss outside.
Worldwide SIMs are OK, in that they operate worldwide, but are pretty expensive in terms of cost/min.
Stuart
